Between 15% and 40% of clothing ordered online is returned, according to various retail reports, and poor fit is the number-one reason. It’s also the reason shoppers inflate their orders, ordering each garment in two sizes, or, overwhelmed with uncertainty, abandon their shopping carts altogether.

Clothes Horse is out to change this. The New York-based startup has gathered a trove of human and brand-garment measurements and combined them with algorithms to help shoppers order garments in the right size. They’ve turned this into a consumer-facing widget retailers can embed on their sites (see above and below).

Clothes Horse is already at work at a number of online retail outlets, including menswear shop Bonobos. When shoppers land on certain product pages, like this one, they are prompted to click on a button that says, “What size am I?” They’ll then be asked to answer a handful of questions about their height and weight, and what sizes they wear in another brand, like J.Crew. After they’ve filled out the questionnaire, Clothes Horse will tell you what size to buy in that product.

In early A/B tests, Bonobos saw a 13% sales increase on product pages that had the Clothes Horse widget installed, according to a joint case study. In instances where shoppers actually filled out the questionnaire, the increase was about triple, Vik Venkatraman, one of Clothes Horse’s three co-founders, says. He was unable to tell me if the return rate on those items was lower.

I asked Venkatraman why he and his team decided to develop a workaround to standardized sizing, rather than find seek out a different solution altogether, a la Indochino (which does made-to-measure suits online) or Acustom (which, when it launches, plans to use body scanners to create custom-fit clothing). “For certain shoppers going custom is a great answer to the problem of fit, but it doesn’t actually solve the problems of all of these terrific brands that have great product and aesthetic, which you miss when you go custom,” he said.

I also asked him what differentiated Clothes Horse from its competitors, like True Fit, a partner of Macy’s. He explained that Clothes Horse’s questionnaire was much faster — 30 seconds versus several minutes (I found this to be true) — and that, as a result, shoppers were more likely to fill it out to completion. “In addition, we make it very easy for new retailers to get started with us in a fast and inexpensive way — with no up-front expense and nearly no work required,” he said. “The TrueFit product, alternatively, takes months of development and much more integration work.”

The startup raised a small, undisclosed round of funding in December of last year, and isn’t actively looking for additional investment, Venkatraman says. Most of its partners to date have been small menswear retailers, though Clothes Horse is also designed to work with womenswear.